I am a moderator for ooo-general-ja/AT/incubator.apache.org.
I have checked the mail archives on mail-archives.apache.org and found that there are 3 non-English language mailing list on mail-archives.apache.org such as dev-br/AT/spamassassin.apache.org, dev-de/AT/spamassassin.apache.org and axis-user-ja/AT/ws.apache.org.
Maybe axis-user-ja/AT/ws.apache.org is the first Japanese language mailing list on Apache. See one of posts from this archive. It's in Japanese encoded ISO-2022-JP but parts of it is garbled. It was posted on Wed. 01 Dec 2004 06:18:12 GMT.
2 Japanese moderators and 2 Japanese volunteer testers are now testing ooo-general-ja/AT/incubator.apache.org.
I hope Japanese be no garbled :)